1. Field of the Invention
The invention relates to fiber manufacturing and, more particularly, to improving performance of a refiner. The invention can be particularly advantageous for monitoring and controlling, for example, a rotary disk refiner.
2. Description of the Related Art
Refiner devices are used to process the cellulose fibers of a fibrous matter prior to delivering the fibrous matter to a machine for manufacturing a fiber product, such as paper. Types of fibrous matter that are typically processed by refiners includes wood chips, pulp, and fabric. One type of refining process is typically referred to as a thermo-mechanical pulp (“TMP”) process, in which abrasive forces are exerted on the fibrous matter to fibrillate the outer layers of the fibers. Refiners used in TMP processing can be arranged in several known configurations, including counter-rotating refiners, double-disc or twin refiners, and conical disc (“CD”) refiners.
Maintaining a specific set of characteristics, such as burst and tear strength, from one batch of fiber products to another is of utmost importance in fiber manufacturing. However, it is difficult to maintain such characteristics in finished fiber products over time, even when specific parameters of the refiner can be monitored. Specifically, although measured refiner parameters may indicate the existence of disturbances in a refiner, known systems are unable to use these measurements to properly respond to these disturbances. One reason for this deficiency is that known control systems do not have the capability to fully characterize refiner disturbances, which can, for example, be related to production, feed consistency, and/or feed water. A production disturbance can be defined as an unexpected change in on-line stock throughput, while a feed consistency disturbance can be defined as an unexpected change in consistency of feed stock as it enters a refiner. A feed water disturbance can be defined as an unexpected change in a mass flow rate of dilution water.
Some known fiber manufacturing control systems include a distributed control system (DCS) that is coupled to multiple refiners in a fiber processing plant and that monitors specific parameters of each refiner. These parameters can include a motor load, a dilution water flow rate, a hydraulic load, a feed screw speed, a refiner case pressure, an inlet pressure, a refiner plate gap, and a refiner consistency. A DCS can also control the operation of a refiner based on measured parameters. For example, when a DCS determines that a measured motor load indicates a disturbance in the refiner, the DCS can attempt to address the disturbance by adjusting the speed of a feed screw, thus changing the on-line throughput of the refiner.
However, adjusting feed screw speed by the DCS may not sufficiently address the disturbance indicated by the detected change in motor load. In the above example, the DCS adjusts only the feed screw speed to address the disturbance based on the assumption that the disturbance is solely production-based. However, in reality, the disturbance may be related to both production and feed consistency, which is not affected by an adjustment to feed screw speed. Rather, feed consistency can be altered by adjusting a flow rate of dilution water or by changing a plate gap distance. As such, the response by the DCS to the disturbance may be improper or deficient.
In another example, when a DCS determines that a measured refiner consistency indicates a disturbance in the refiner, the DCS can attempt to address the disturbance by adjusting the dilution water flow rate, thus changing the feed consistency of the refiner. If the refiner consistency is held at a constant value, then any remaining motor load disturbance is then attributed to production and addressed by adjusting the speed of a feed screw. While this control strategy effectively eliminates the feed consistency and production disturbance, it requires a specific, rigid, control strategy. Thus, this control method only applies to refiners in which a feed screw speed can be adjusted, such as primary refiners.
Known systems are unable to measure or otherwise characterize production disturbances and feed consistency disturbances. Thus, such systems are unable to accurately adjust the operation of a refiner in response to such disturbances using a multivariable control approach that does not require a specific, rigid, control strategy and a feed screw with an adjustable speed. As a result, both manually-controlled processes and DCS-based processes rely on post-processing pulp quality feedback to make corrections for disturbances in production and feed consistency.